In RFID systems widely employed in recent years, both a mobile electronic apparatus and a reader/writer in a mobile phone, or other equipment, incorporate an antenna for information communication in which data is exchanged between them. In particular, it is strongly desired that an antenna incorporated in a mobile electronic apparatus achieve high performance, be inexpensive, and be small. Japanese Patent No. 3772778 (Patent Document 1) discloses a magnetic material antenna including a magnetic material core as one example that attempts to meet these requirements.
FIG. 1 is a perspective view of a magnetic material antenna illustrated in Patent Document 1. This antenna 10 includes a core member (magnetic material core) 12 and a single electrical insulating film (flexible substrate) 14 having a first principal surface on which a spiral section 13a is formed by a continuous first conductor (coil conductor) 13. A second conductor 15 is formed on a second principal surface of the electrical insulating film 14, and an end of this second conductor 15 and an end of the first conductors 13 are connected to an IC chip 16.
However, with the configuration illustrated in FIG. 1, the coil conductor formed at a bend of the flexible substrate 14 is adjacent to the end face of the magnetic material core 12, so the effect of magnetic flux closed in the vicinity of the coil conductor tends to cause an excess of self-inductance. Because of this, when an antenna is realized under the constraint of a constant self-inductance value, the problem arises of a reduced number of turns of the coil and a decreased sensitivity of the antenna. Additionally, because blocking part of a magnetic-flux transmitting surface of the magnetic material with part of the coil conductor reduces the size of an opening of the antenna, the problem arises of a reduction in the distance in which communications are possible.